#include<stdio.h>
int main(){
	/*int x = 3;
	int y = 3;
	switch (x % 2) {
	case 1:
		switch (y)
		{
		case 0:
			printf("first");
		case 1:
			printf("second");
			break;
		default: printf("hello");
		}
	case 2:
		printf("third");
	}*/

	/*return 0;*/
	/*int a = 1;
	int b;
	switch (a)
	{
	case 1: b = 30;
	case 2: b = 20;
	case 3: b = 16;
	default: b = 0;
	}
	return b;*/
	int a = 0, b = 0;
	for (a = 1, b = 1; a <= 100; a++)
	{
		if (b >= 20) break;
		if (b % 3 == 1)
		{
			b = b + 3;
			continue;
		}
		b = b - 5;
	}
	printf("%d\n", a);
	return 0;
}